Cathode ray tube



Feb. 2, G N OGLOBUNSKY 2,969,460

CATHODE RAY 'TUBE Filed Sept. 30, 1933 Patented Feb. V2, '1937 PATENT OFFICE CATHODE RAY TUBE Gregory N. Ogloblinsky, deceased, late of Collingswood, N.,J., by Vladimir K. Zworykin, ad-

ministrator, Philadelphia, Pa.,

assignor to Radio Corporation of America, a corporation oi' Delaware Application september so, 1933, serial No. 691,671

Claims.

This invention relates to improvements in television systems.

In television systems embodying a cathode ray tube at the transmitting station, and in which the tube comprises a photosensitive mosaic screen on which an image of the object is projected, and which is scanned by a cathode ray, it has been found to be advantageous to project the image on the same side of the screen which is scanned by the ray. VWhen this is done, the axis of the optical system for projecting theimage is usually made perpendicular to the screen, but the axis of the so-called gun for developing and directing the ray of electrons is, for convenience, disposed atan angle to the screen. On account of this arrangement, the outline of the area scanned by the ray has a keystone shape rather than the desired rectangular shape. This distortion of the scanned pattern is manifested by a substantial and corresponding distortion of the reproduced image at the receiving station, the reproduced image being also the shape of a keystone, with the vertical lines inclined downwardly towardeach other. l

With the foregoing in mind, it is one of the objects of the invention to provide an improved television system of the character referred to wherein the keystone distortion is corrected.

Other objects and advantages will hereinafter appear.

In accordance with the invention, the cathode ray at the transmitting station is deflected in such manner as to tend to spread out the scanned pattern in a keystone effect opposite to the keystone pattern which would` otherwise be scanned, the effect being to substantially entirely compensate vor correct for the latter, so that the scanned pattern is rectangular in shape.

`More particularly, in accordance with the invention, complementary plates are used to defiect the cathode ray at the higher frequency, sometimes referred to as the line frequency. The edgesof these plates nearer to the screen are cut on 'a bias in such manner and amount to cause the amplitude of deflection to vary uniformly during each scanning period. In this way,

, each line is made slightly shorter by the same amountv from each end thereof than the preceding line, to cause the ray to scan a keystone area in a. plane perpendicular to the tube axis, the sides of this area being inclined upwardly toward each other. When the ray strikes the inclined screen, therefore, and is deflected in the two directions at right angles to each other, it

(Cl. Z50-27.5)

is caused to scan the screen over a rectangular area.

The invention resides in the improved apparatus of the character hereinafter described and claimed.

For the purpose of illustrating the invention, an embodiment thereof is shown in the drawing, wherein Figure 1 is a perspective view, partly diagrammatic, of a transmitting tube constructed and operating in accordance with the invention;

Fig. 2 is a simplified, front elevational view, taken from Fig. l;

Fig. 3 is a plan view of Fig. 2;

Fig. 4 is a sectional view, the section being taken on the line 4--4 in Fig. 2; and

Fig. 5 is a diagrammatic view illustrative of the principle of operation.

In Fig. 1, a transmitting tube III is provided with an electrode I2 having a photosensitive surface I4 comprised of a great number of minute metallic elements, such as silver globules, each insulated from the electrode I2 and from each other, and each provided with a coating of photosensitive material. In operation, an image of the object, shown as being in the form of a moving picture film I6, is projected upon the photosensitive surface by a suitable optical system I'I, the axis I8 of the optical system being perpendicular to the screen surface I4.

A gun 20 of any suitable construction operates to develop and direct a ray 24 of electrons at the photosensitive surface I4, the axis 22 of the gun being disposed at an angle, for example 60 degrees, to the photosensitive surface I4.

For the purpose of causing the ray 24 to scan the photosensitive surface of the screen I2, a saw-tooth voltage wave at a frequency of 24 cycles, for example, is applied across complementary plates 26, and a saw-tooth voltage wave at a frequency of 4320 cycles, for example, is applied across complementary plates 28. The ray, therefore, is deflected vertically 24 times a second by the plates 26, and is simultaneously deflected horizontally 4320 times a second by the plates 28. The plates 26 and 28 are disposed within the tube, as represented, and may be carried by supporting elements (not shown) extending from the structure of the gun 20.

In operation, the projection of the image on the photosensitive surface I4 causes discrete electrostatic charges to be stored up over the surface, each elemental charge being proportionate to the light intensity at the elemental area. As the ray 24 scans the surface I4, these charges are 55 neutralized to .develop picture signals which are supplied to a radio or other transmitting system, (not shown).

Ordinarily, the ray 24 would scan the surface Il over an area ABCD, as shown in Fig. 5. That is, the scanning pattern would be the shape of a keystone rather than the desired rectangle. This would cause, at the receiving station, the production of a distorted image on the fluorescent screen of the usual cathode ray tube, the vertical lines of the reproduced image being so inclined to each other that the entire image would have a generally keystone conguration.

For the purpose of compensating or correcting for the keystone distortion referred to, it is proposed to shape and position the plates 28 in the following manner. These plates are on opposite sides of the axis 22 of the tube and the edges 28d thereof nearer to the screen I2 are cut on a bias. as more clearly shown in Fig. 2.

For the purpose of providing clearance for full horizontal deflection of the ray between the two extreme positions W and X, the plates 28 are made to diverge outwardly from each other in the direction looking toward the screen l2, as more clearly shown in Fig. 3. The edges 28e, which are nearer to the gun 20, are, therefore, closer together than the edges 28d.

Likewise, for the purpose of providing clearance for full vertical deflection of the ray between the two extreme positions Y and Z, the plates 26 are made to diverge outwardly from each other in the direction looking toward the screen i2, as more clearly shown in Fig.- 2. The edges 26o of the plates, which are nearer to the gun 20, are therefore closer together than the edges 26d.

In operation of the tube, as the ray is deilected horizontally and simultaneously deflected vertically downward, the amplitude of any horizontal deflection is slightly greater than the amplitude of the preceding horizontal deflection. 'I'he ray 24, therefore, is caused to scan a keystone area such as EFGH in Fig. 5, in a plane perpendicular to the axis 22 and which is about the same distance from the gun 2U as the screen I2. The result is that the ray scans the screen i2 over the desired rectangular area such as is represented in Fig. by the area JKLM.

The action just described is attributed to the fact that, for the same conditions of voltage, the amplitude of deflection of a cathode ray by plates is directly proportional to the distance along the plates where the ray is at the instant. That is, with pairs of plates similarly spaced but of different length, the pair of longer plates will deflect the ray more than the pair of shorter ones, the difference corresponding to the difference in length of the plates. It will, therefore, be apparent that when the ray is between the upper edge portions of the plates 28 the amplitude of horizontal deflection will be a minimum, and when the ray is between the lower edge portions of the plates, the amplitude of horizontal deilection will be a maximum,

In the drawing, the screen I2 is considered to be substantially eight inches from the tip of the gun 20, and to be inclined 60 degrees to the axis 22. With regard to the respective angles of inclination of the plates 26 and 28, these are determined according to the various dimensions and reguirements of any particular tube. In the particular tube shown, satisfactory results have been obtained with the respective angles about as shown and designated.

For a receiving tube, the embodiment of the invention would be the same as in the transmitting tube disclosed, but the front surface of the screen l2 would be coated with uorescent material, and the optical system I1 would be one which would project onto a relatively large, external screen, the image reproduced on the fluorescent screen.

From the foregoing it will be seen that there has been provided improved cathode ray apparatus wherein the screen is inclined substantially to the axis of the tube, and wherein the ray is caused to scan the screen over a substantially rectangular area by the action of at least one pair of plates which deflect the ray at the higher, linefrequency. In this connection, it will be understood that electromagnetic coils can be used instead of the plates 26 for deecting the ray at the lower orl frame-frequency.

While but one embodiment of the invention has been described, it will be understood that various modiilcations are possible without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

1. A cathode ray tube comprising a substantially iiat screen and means for developing a scanning ray and directing the same at said screen, the axis of said ray-developing means being inclined at an angle to said screen whereby the part of the latter on one side of said axis is closer to said ray-developing means than the other part of said screen, and means for deflecting said ray simultaneously in different directions at relatively high and relatively low frequencies respectively to cause the ray to scan said screen over a substantially rectangular area, said defiecting means including complementary plates for deflecting the ray at the relatively high frequency and disposed within the tube on opposite sides of said axis, the adjacent edges of said plates on opposite sides of said axis being cut on a bias with respect to a plane perpendicular to said axis.

2. A cathode ray tube comprising screen structure, means for scanning said structure comprising means for developing a scanning ray and directlng the same at said structure, the axis of said ray-developing means being inclined at an acute angle to said structure, and means for deiiecting said ray simultaneously in different dlrections at relatively high and relatively low frequencies respectively to cause the ray to scan said structure over a substantially rectangular area, said defiecting means including complementary plates disposed on opposite sides of said axis for deilecting the ray at the relatively high frequency, the distance between said plates measured along said axis varying uniformly.

3. A cathode ray tube comprising a substantially fiat screen and means for developing a scanning ray and directing the same at said screen, the axis of said ray-developing means being inclined at an acute angle to said screen whereby the part of the latter on one side of said axis is closer to said ray-developing means than the other part of said screen, and means for deecting said ray simultaneously in different directions at relatively high and relatively low frequencies respectively to cause the ray to scan said screen overa substantially rectangular area, said deflecting means including complementary plates disposed on opposite sides of said axis for deflecting the ray at the relatively high frequency,

. the distance between said plates measured along v said axis increasing uniformly from one side of said axis to the other side thereof.

4. A cathode ray tube comprising a substantially flat screen and means for developing a scanning ray and directing the same at said screen, the axis. of said ray-developing' means being inclined at an angle to said screen whereby the part of the latter on one side of said axis is closer to said ray-developing means than the other part of said screen, and means for deflecting said ray simultaneously in diierent directions at relatively high and relatively low frequencies respectivelyto cause the ray to scan said screen over a. substantially rectangular area, said deiiecting means including complementary plates for deiiecting the ray at the relatively high frequency and disposed within the tube on opposite sides of said axis, the adjacent edges of said plates on opposite sides of said axis being inclined thereto.

l5. A cathode ray tube comprising a substantially flat screen and means for developing a scanning 'ray and directing the same at said screen, the axis of said ray-developing means being inclined at an angle to said screen whereby the part oi the latter on one side of said axis is closer to said ray-developing means than the other part of said screen, and means for deflecting said ray' simultaneously in different directions at relatively high and relatively low frequencies respectively to cause the ray to scan said screen over a substantially rectangular area, said deilecting means including complementary plates for deflecting the ray at the relatively high frequency and disposed within the tube on opposite sides of said axis, the adjacent edges of said plates on opposite sides of said axis being inclined thereto at an angle of the order of forty degrees.

- VLADIMIR K. ZWORYKIN.

Ogloblnsky, Deceased. 

